The present invention is directed to a fluid supply and fluid handling mechanism for an intravascular heat exchanger, and more particularly to a disposable cassette with a pump head and an external heat exchanger for use as a system to provide hot or cold heat transfer fluid to an intravascular heat exchange catheter.
Under ordinary circumstances, thermoregulatory mechanisms exist in the healthy human body to maintain the body at a constant temperature of about 37xc2x0 C. (98.6xc2x0 F.), a condition sometimes referred to as normothermia. To maintain normothermia, the thermoregulatory mechanisms act so that heat lost to the environment is replaced by the same amount of heat generated by metabolic activity in the body.
For various reasons, however, a person may accidentally develop a body temperature that is above or below normal, conditions known as hyperthermia or hypothermia respectively. These conditions have generally been regarded as harmful and patients suffering from either condition have been treated to return them to normothermia by various mechanisms, including application of warming or cooling blankets, administration of hot or cold liquids by mouth, hot or cold liquids infused into the bloodstream, immersion of the patient in hot or cold baths, and directly heating or cooling blood during cardiopulmonary bypass.
Besides treating undesirable hypothermia to reverse the condition and restore normothermia, medical science recognizes that it is sometimes valuable to intentionally induce and maintain regional or whole body hypothermia for therapeutic reasons. The term xe2x80x9cwhole body hypothermiaxe2x80x9d refers to the condition where the whole body temperature, usually measured as the core body temperature, is below normothermia. xe2x80x9cRegional hypothermiaxe2x80x9d refers to the condition where target tissue of one region of the body such as the brain or the heart is maintained at a temperature below normothermia. During regional hypothermia, the core body temperature may be normothermia, or may be slightly hypothermic but is generally warmer than the target tissue.
It may be desirable, for example, to induce whole body or regional hypothermia for the purpose of treating, or minimizing the adverse effects of, certain neurological diseases or disorders such as head trauma, spinal trauma and hemorrhagic or ischemic stroke. Additionally, it is sometimes desirable to induce whole body or regional hypothermia for the purpose of facilitating or minimizing adverse effects of certain surgical or interventional procedures such as open heart surgery, aneurysm repair surgeries, endovascular aneurysm repair procedures, spinal surgeries, or other surgeries where blood flow to the brain, spinal cord or vital organs may be interrupted or compromised. Neural tissue such as the brain or spinal cord, is particularly subject to damage by blood deprivation for any reason including ischemic or hemorrhagic stroke, cardiac arrest, intracerebral or intracranial hemorrhage, and head trauma. In each of these instances, damage to brain tissue may occur because of brain ischemia, increased intracranial pressure, edema or other processes, often resulting in a loss of cerebral function and permanent neurological deficits. Hypothermia has also been found to be advantageous to protect cardiac muscle tissue during or after ischemia, for example during heart surgery or during or after a myocardial infarct.
Traditional methods inducing and/or maintaining hypothermia include application of surface cooling such as an ice bath or cooling blankets, infusing cold liquid into the vascular system of a patient, or controlling the temperature of a patient""s blood during cardiopulmonary bypass. While each of these may be useful in certain settings, they each have significant disadvantages. For example, inducing hypothermia by placing a patient into a cold bath lacks precise control over a patient""s core temperature and thus may result in harmful overshoot, which may be difficult if not impossible to reverse with any degree of control. It generally cannot be used in conjunction with surgery because sterility and access to the patient""s body may make its use impractical or impossible. Cooling blankets are often too slow to cool the patient, or simply unable to overcome the body""s natural ability to generate heat, particularly if the patient is shivering or experiencing vasoconstriction. Even if the patient is anesthetized, or has otherwise had his thermoregulatory responses impaired or eliminated, cooling by means of cooling blankets is still often too slow and inefficient to be useful. Control over the patient""s temperature is generally poor, which is particularly dangerous if the patient""s own thermoregulatory controls are eliminated or impaired.
Infusion of cold or hot fluid into a patient""s bloodstream has also been used to affect the temperature of a patient. However, this procedure is severely limited because of the hazards of fluid loading. Particularly where hypothermia is to be maintained for a long period of time, continuous infusion of sufficient cold liquid to counter the heat generated by ordinary bodily activity creates an unacceptable amount of fluid introduced into the body. In addition, as with the methods described above, control over the patient temperature is limited.
Another method sometimes employed, especially during heart surgery, is cardiopulmonary bypass, where blood is removed from the body, oxygenated and returned to the circulatory system by means of a mechanical pump. While being circulated outside the body, the temperature of the blood may be controlled by directly heating or cooling it and then pumping it back into the body, and in this way the temperature of the entire body of the patient may be controlled. Because of the large volume of blood removed, treated, and pumped back into the body, heating or cooling the body by means of cardiopulmonary bypass is very rapid and may be precisely controlled. However, the use of an external mechanical pump to circulate blood tends to be very destructive of the blood and thus physicians try to minimize the time on which the blood is being subjected to this treatment, preferably to four hours or less. Furthermore, the situations in which the use of this method for temperature control is very limited because of the extremely invasive nature of cardiopulmonary bypass. The patient must be anesthetized, highly trained personnel are required, and the procedure is only available in an operating room or similarly equipped facility.
Intravascular heat exchangers have been developed to control patient temperature for either treating hypothermia or hyperthermia or inducing and maintaining hypothermia. The intravascular heat exchanger overcomes many of the shortcomings of the above mentioned methods while permitting the advantageous aspects of controlling patient temperature. The intravascular heat exchanger comprises a catheter in which heat transfer fluid is circulated between an external heat exchanger, such as a solid state thermoelectric plate of one or more Peltier cooling units and a heat transfer region such as a balloon region on the end of the catheter. The heat exchange region is inserted into the vasculature of a patient. The heat transfer fluid exchanges heat with the blood at the heat transfer region to change the temperature of the blood and thus of the patient. The heat transfer fluid is then circulated out of the body and exchanges heat with the external heat exchanger outside the body to add or remove the heat lost or gained from the blood. In this manner the temperature of the blood and ultimately of the patient may be controlled by controlling the temperature of the external heat exchanger.
Some intravascular heat exchange catheters may be designed to affect a small amount of tissue, for example a small bolus of blood in thermodilution catheters (see e.g. Williams, U.S. Pat. No. 4,941,475) or catheters designed to protect or affect the tissue in contact with the catheter (see e.g. Neilson, et al., U.S. Pat. No. 5,733,319). However, intravascular heat exchangers designed to affect whole or regional body temperature may be expected to exchange a significant amount of energy, for example more than 100 watts. This is achieved by maintaining a maximum difference in temperature between the blood and the heat transfer region (xcex94T), and flowing a maximum amount of heat exchange fluid through the circuit. A heat exchange fluid that can be maintained between 0xc2x0 C. and 45xc2x0 C. is generally preferable, along with a fluid supply system that can supply adequate flow of heat transfer fluid and temperature control of that fluid. Such systems ideally will also have one of more of the following properties: maximum external heat exchange ability, closed circuit for sterility, small volume for precise and rapid control of temperature, a system for pressure regulation to precisely control flow rate, optimal flow rate, disposable features, ease of handling, and reliability.
One aspect of the invention is a heat exchange fluid supply system for supplying a heat exchange fluid to an intravascular heat exchange catheter, which includes a disposable cassette having a pump head and an external heat exchanger. The configuration of the external heat exchanger is not intended to be structurally limited and may include a sack-like configuration, a relatively flat configuration with multiple paths therein, with a long serpentine path therein, or any other suitable configuration capable of mating with a heat generating or removing unit. The system may be configured to operate in combination with a reusable master control unit and an external fluid source.
Another aspect of the invention is a disposable cassette for supplying a heat exchange fluid to a heat exchange catheter, the cassette comprising: an external heat exchanger comprising a flow channel having an inlet and an outlet; a first fluid supply line, the first fluid supply line being in fluid communication with the flow channel inlet; a pump head contained in the disposable fluid supply cassette, and having a pump inlet and a pump outlet, where the pump inlet is in fluid communication with the external heat exchanger flow channel outlet for pumping fluid from the external heat exchanger flow channel outlet; a second fluid supply line, the second fluid supply line being in fluid communication with the pump outlet for receiving fluid pumped out of the pump outlet; and a pressure regulator, the pressure regulator being in fluid communication with the pump outlet for regulating the pressure of fluid pumped from the pump head.
Yet another aspect of the invention is a heat exchange fluid supply system for a heat exchange catheter, the system comprising: an external heat exchanger comprising a structural member and a compliant member, where the compliant member is sealed to the structural member in a pattern, the pattern forming a flow channel between the compliant member and the structural member, and the flow channel having an inlet and an outlet; a first fluid supply line, the first fluid supply line being in fluid communication with the flow channel inlet; a bulkhead, the bulkhead comprising a pump head and a reservoir, the reservoir having a reservoir inlet and a reservoir outlet, the reservoir inlet being in fluid communication with the external heat exchanger flow channel outlet, the pump head having a pump inlet and a pump outlet, the pump inlet being in fluid communication with the reservoir outlet for pumping fluid from the reservoir outlet; a second fluid supply line, the second fluid supply line being in fluid communication with the pump outlet for receiving fluid pumped out of the pump outlet; and an external fluid source, the external fluid source being in fluid communication with the bulkhead.
Still another aspect of the invention is a disposable cassette for supplying heat exchange fluid to a heat exchange catheter, the cassette comprising: an external heat exchanger having an inlet and an outlet; a first fluid supply line, the first fluid supply line in fluid communication with the heat exchanger inlet; a disposable pump head contained in the cassette, the pump head actuated by an electric motor, the pump head having an inlet and an outlet, and the pump inlet being in fluid communication with the heat exchanger outlet; a second fluid supply line, the second fluid supply line being in fluid communication with the pump outlet for receiving fluid pumped out of the pump outlet; and an optional pressure regulator, the pressure regulator being in fluid communication with the pump outlet for regulating the pressure of fluid pumped from said pump head.
Another aspect of the invention is a disposable cassette for supplying a heat exchange fluid to an intravascular heat exchange catheter, the cassette having a bulkhead and an external heat exchanger. The external heat exchanger has a thin heat exchanger layer and a back plate fused together to form a serpentine flow channel or a plurality of flow channels, and has an inlet orifice and an outlet orifice that allow fluid to circulate through the external heat exchanger and which communicate with the bulkhead. In one embodiment, the bulkhead has three components which can be independent sections coupled together or where at least two of the sections are housed together: a reservoir section, a feedblock section and a pump section. The reservoir section has an inlet hole leading from the external heat exchanger and an outlet leading to the feedblock section, a fluid reservoir for storage of heat exchange fluid, a fluid level detector for monitoring the level of heat exchange fluid within the fluid reservoir, a cover plate that functions to retain fluid within the reservoir and which is fitted with at least one vent hole into which is positioned a hydrophobic vent for releasing air contained within the fluid reservoir. The feedblock section has a central chamber which houses a priming valve that directs fluid flow, an inlet and corresponding inlet channel from the reservoir and an inlet and corresponding inlet channel from an external fluid source which both lead into the central chamber, an outflow channel leading from the central chamber to an outlet which is directed to the pump head, a flexible membrane covering the central chamber, a flow-through channel having an inlet which leads from the pump head and a fluid coupling outlet means for fluidly connecting the catheter to the bulkhead, and a flow-through channel having a fluid coupling inlet means for fluidly connecting the catheter to the bulkhead and an outlet which leads to the pump section and then to the external heat exchanger. The pump section has a quasi-cardioid shaped cavity, into which is positioned a rotor is fitted with a vane for moving fluid from an inlet and inlet channel to an outlet channel and outlet, a wheel assembly to facilitate movement of the rotor and a flow-through channel having an inlet that leads from the feedblock section and an outlet which leads to the external heat exchanger.
In yet another aspect of the invention, the bulkhead has two components: a reservoir section and a pump section, where the pump and reservoir sections are configured similar to that described above, except that the outlet of the reservoir section leads to the pump section and the reservoir further comprises a pressure damper and an inlet in fluid communication with an external fluid source.
Still another aspect of the invention relates to a cassette for supplying heat exchange fluid to a heat exchange catheter, where the cassette comprises: (a) an external heat exchanger comprising a structural member and a compliant member, where the compliant member is sealed to the structural member in a pattern that forms a flow channel between the compliant member and the structural member, and where the flow channel has an inlet and an outlet; (b) a first fluid supply line in fluid communication with the flow channel inlet; (c) a bulkhead comprising a reservoir and a disposable pump head, where the reservoir contains an inlet in fluid communication with the flow channel outlet, and further has a fluid level detector for detecting the level of fluid within the reservoir, wherein the pump head is a cardioid vane pump head having an inlet and an outlet, and the pump head is actuated by an electric motor, where the pump inlet is in fluid communication with the reservoir outlet and the electric motor is controlled by an amplifier controller, where the amplifier controller supplies a constant current to the pump head thereby causing the pump head to supply a relatively constant pressure to the fluid in the second fluid supply line; (d) a second fluid supply line in fluid communication with the pump outlet for receiving fluid pumped out of the pump outlet; (e) an external fluid source in fluid communication with the reservoir; and (f) a pressure damper in fluid communication with the pump outlet.
Another aspect of the invention pertains to a method for providing a temperature regulated source of heat exchange fluid for heat exchange catheters, comprising the steps of: providing a circuit comprising an external heat exchanger, a pump, a heat exchange catheter, and air vents, where the external heat exchanger, pump and heat exchange catheter are in fluid communication such that fluid pumped by the pump is circulated through the heat exchange catheter and the external heat exchanger, and the air vents allow passage of gas in and out of the circuit through the vents but do not allow passage of liquid in and out of the circuit though the air vents; providing a heat generating or removing unit in heat exchange relationship with the external heat exchanger; providing an external fluid source in fluid communication with the circuit; circulating heat exchange fluid from the external source through the circuit by means of pumping with the pump while simultaneously venting any gas contained in the circuit out through the air vents; and controlling the temperature of the heat exchanger fluid in the circuit by controlling the temperature of the heat generating or removing unit.